Disposable solid fuel rocket motors are known, but such motors are inherently subject to a variety of potential problems, including issues of safety, environmental pollution resulting from improper disposal of spent or used motors and the additional cost associated with the need to use new parts for the next firing of the motor.
A rocket motor which may be reloaded and reused is disclosed in U.S. Pat. No. 5,212,946 of Paul C. Hans et al, which issued May 25, 1993. Such a motor is stated to be of modular design, and to permit the user to vary the performance of the motor by using interchangeable nozzles of various designs, different length casings, diverse propellant charges and sizes, different ejection charge delays and different ejection charge power.
In assembly of a typical modular rocket motor, propellant grains are inserted into a liner. The propellant grains are solid and in the form of a right cylindrical column with a central bore i.e. with an axial orifice through the column of propellant grains. Typically, one or more propellant grains are inserted end-to-end into the liner, which is of an appropriate length with respect to the number of propellant grains being inserted. The liner is formed of cardboard, and is not intended to be re-used in subsequent firings of the rocket motor.
The liner with inserted propellant grain is inserted into a motor casing and sealed against pressure leaks using a plurality of O-rings. A nozzle system is inserted in one end of the casing, and a forward closure assembly having a delay charge for activation of a parachute system is inserted into the other end of the casing.
While such a system is useful, it typically requires substantial effort in order to clean the motor casing after use, particularly including difficulties in removing all of the charred remains of the liner and residues of propellant grain from the casing so that a new liner may be inserted on reloading of the casing. In addition, typical reloadable motor systems have a significant number of parts, including O-rings, which makes shipping, assembly and disassembly a more complicated operation.